Certain devices such as wafer defect scanners, laser printers, document scanners, projectors and the like employ a collimated laser beam that scans across a flat surface in a straight line or curved path. These devices employ tilting mirrors to deflect the beam to perform the scanning. These tilting mirrors may be, or may include, Micro Electro Mechanical Systems (“MEMS”) devices. The actuation of mirrors used in MEMS devices, referred to herein as MEMS mirrors, can be via the electromagnetic, electrostatic, piezoelectric, and thermoelectric effects, depending on application.
One type of common MEMS mirror includes a stator and a rotor, with the rotor or structures carried by the rotor being reflective. The stator and/or rotor are driven with a drive signal which results in the rotor oscillating with respect to the stator, thereby changing the angle of reflectance of an incident light beam on the rotor. By oscillating the rotor between two orientations, an opening angle of the mirror is defined, and scanning of the light beam across the flat surface is accomplished.
Precise control of the opening angle of the mirror so as to maintain the opening angle at a constant angle is desirable for the precise application in which such MEMS mirrors are used. However, current mirror driving techniques may not provide for a constant opening angle when operating conditions or properties of the circuitry change. Therefore, further development is needed.